So why do men and perform so differently in combat-related tasks? First, physiologically and psychologically, women and men are significantly different. Men are not simply bigger women with different plumbing. Men’s blood carries 10 to 12 percent more oxygen per liter than does a women’s; and men’s VO2 max, a measure of the top rate of oxygen consumption, is 40 to 60 percent greater than that of women. An average fit man will weigh about 23 percent more, have 50 percent more muscle mass, and carry 10 percent less body fat than an average fit woman. Pound for pound, men have thicker skulls, bigger, stronger necks, hearts that are 17 percent larger, and bones that are both bigger and denser. Despite being much heavier, men’s vertical leap is nearly 50 percent greater than that of women.

In terms of reflexes and reaction times, men significantly outperform women. When confronted with immediate danger, studies suggest men are “more likely than women to take action.” Women are far more likely to experience motion sickness and vertigo. In the Navy women go on sick call 60 to 70 percent more frequently. For the kind of violent events and situations found on the battlefield, women are far more likely to develop post-traumatic stress disorder and experience the symptoms for a longer duration than men. Despite the gender-specific ability to handle the pain of childbirth, “study after study” conclusively shows that men have a much overall higher tolerance for pain than women.

Individually, any one of above differences could make the difference between life and death. In the combat environment, the differences between men and women in speed, strength, endurance, agility, physical resiliency, and psychological resiliency represents an unbridgeable gap — and the impact on the battlefield is dramatic.